Adhesion of coatings using adhesive bonding compositions

ABSTRACT

A multi-layer article ( 1 ) disclosed herein contains a metallic substrate ( 2 ), a protective layer ( 6 ), and an adhesive bonding layer ( 14 ) including an oxygen-containing compound that bonds the adhesive bonding layer to the metallic substrate, the protective layer, or both. A method for forming the multi-layer article includes the steps of heating a protective bonding composition ( 20 ) to form a molten material ( 24 ) in contact with a metal-containing surface ( 2 ), allowing the molten material to cool and solidify into the adhesion bonding layer ( 14 ) affixed to the metal-containing surface, depositing a ceramic material ( 26 ) onto the adhesive bonding layer, and heating the ceramic material to form the protective layer ( 6 ) affixed to the adhesive bonding layer.

FIELD OF THE INVENTION

This invention relates generally to the field of materials technology, and more particularly to the fabrication and repair of multi-layer metallic articles containing adhesive coatings.

BACKGROUND OF THE INVENTION

Hot section components of modern gas turbine engines are often made of high-temperature alloys including superalloys based on nickel, iron and cobalt. Cast superalloys (e.g., 247, 738, CMSX4, Rene 5, etc.) and high performance wrought alloys (e.g., X, 625, 617, etc.) are often used in such high-temperature applications (e.g., turbine blades, vanes, combustion transition liners). These superalloys have been developed to withstand increasingly higher operating temperatures as well as the presence of corrosive and oxidative conditions. To withstand these extreme environments, protective coating systems are often applied to the surface of superalloy components to form multi-layer articles. These coating systems include an environmental coating, which can also serve as a metallic bond coat layer, and usually a ceramic thermal barrier coating (TBC) overlying the environmental or bond coat layer.

Such environmental coatings (or bond coats) are typically metallic overlay coatings of the formula “MCrAlX” (where M is a Group VIIIB element such as Co, Ni, or a mixture thereof, and X is a rare earth element such as Y, Hf, W, Zr, La, or a mixture thereof) or diffusion aluminide coatings such as NiAl or a modified NiAl that includes an element such as Pt, Rh or Pd. In thermal barrier coating (TBC) systems containing both a metallic bond coat and a ceramic TBC layer, the TBC layer is often formed from metal oxides such as yttria-stabilized zirconias (YSZs). One of the purposes of the bond coat layer in a TBC system is to improve adhesion between the outer TBC layer and the underlying substrate being protected.

In such multi-layered coating systems, adhesion of the outer protective layer to the underlying metallic substrate is an important consideration that can greatly affect the efficiency and longevity of a hot section component. Protective coatings are subject to degradation as a function of service. Elevated temperatures, high stresses (both sustained and cyclic), reactions with process gas, and foreign object impact can cause a variety of chemical and physical property changes leading to loss of coating (via e.g. cracking and spalling) resulting in exposure of the underlying substrate and further component damage.

FIG. 1 illustrates one non-limiting example in which a superalloy substrate 2 protected by a multi-layered TBC system 8, comprising an inner MCrAlY bond coat layer 4 and an outer ceramic TBC layer 6, is compromised through degradation of the outer ceramic TBC layer 6 leading to erosion 12 of both the bond coat layer 4 and the underlying superalloy substrate 2. In this illustration the missing portion 10 of the TBC layer may have occurred due to relatively poor adhesion between the outer ceramic TBC layer 6 and the inner MCrAlY bond coat layer 4.

A need exists to somehow improve adhesion between these outer protective layers 4, 6 and the underlying substrate 2 to improve component longevity and efficiency.

BRIEF DESCRIPTION OF THE DRAWINGS

The invention is explained in the following description in view of the drawings that show:

FIG. 1 illustrates damage that can occur to an underlying metallic substrate when a protective coating is damaged or degraded.

FIG. 2 is a cross-sectional view of a multi-layer article containing a metallic substrate, an adhesive bonding layer, and a ceramic protective layer, according to one embodiment.

FIG. 3 is a cross-sectional view of a multi-layer article containing a metallic substrate, a bond coat layer, an adhesive bonding layer, and a ceramic protective layer, according to one embodiment.

FIG. 4 is a cross-sectional view of a multi-layer article containing a metallic substrate, a ceramic protective layer, and a plurality of chemical anchors bonded to both the metallic substrate and the protective layer, according to one embodiment.

FIG. 5 is a cross-section view of a multi-layer article containing a metallic substrate, a bond coat layer, a ceramic protective layer, and a plurality of chemical anchors bonded to both the bond coat layer and the ceramic protective layer, according to one embodiment.

FIG. 6 is a photograph illustrating a spear-like cuspidine crystal, according to one embodiment.

FIG. 7 illustrates process steps of a method for forming a multi-layer article, according to one embodiment.

FIG. 8 illustrates process steps of a method for forming a multi-layer article, according to one embodiment.

FIG. 9 illustrates process steps of a method for forming a multi-layer article, according to one embodiment.

DETAILED DESCRIPTION OF THE INVENTION

The inventors were aware that certain welding and cladding flux formulations produce slag deposits that are difficult to remove. This adhesion is generally considered to be problematic in the welding industry—especially with multi-pass welds where it becomes both labor intensive to remove the deposits and where incomplete removal can result in the formation of inclusions and inferior weld deposits. For this reason welding compositions (e.g., flux compositions) are generally formulated to enhance detachability of the resulting slag deposits, see, e.g., Oladipupo, A. O., “Slag Detachability from Submerged Arc Welds,” Doctoral Thesis (Massachusetts Institute of Technology) February 1987 and US 2006/0266799.

Although contrary to the accepted wisdom in the relevant art, the inventors recognized a possible utility of welding compositions capable of forming such deposits having low detachability, as a way to improve adhesion between protective coating systems and underlying metallic substrates. It was also envisioned that certain deposits could also be formulated to provide protective features that either supplement the outer protective layer (e.g., TBC/bond coat) or replace it altogether. Based upon this recognition, the inventors have developed protective bonding compositions and methods for using such compositions in the fabrication and repair of multi-layer articles having improved adhesion between protective outer layer(s) and underlying metallic substrates.

FIG. 2 is a cross-sectional view of a multi-layer article 1 according to one embodiment. In this non-limiting example the multi-layer article 1 comprises a metallic substrate 2 bonded to an adhesive bonding layer 14 that is covered by a protective layer 6. Unlike previously reported coating systems, the multi-layer article 1 of this embodiment does not contain an intermediate bond coat layer—but instead relies upon the adhesive bonding layer 14 which is a non-MCrAlY deposit having low detachability as briefly described above and further described in greater detail below.

The metallic substrate 2 of FIG. 2 (as well as in other embodiments described and implied below) may be a ferrous substrate (e.g., stainless steel) or a non-ferrous substrate such as a superalloy. The term “superalloy” is used herein as it is commonly used in the art, i.e., a highly corrosion and oxidation resistant alloy that exhibits excellent mechanical strength and resistance to creep at high temperatures. Superalloys typically include a high nickel or cobalt content. Examples of superalloys include alloys sold under the trademarks and brand names Hastelloy, Inconel alloys (e.g. IN 100, IN 700, IN 713, IN 738, IN 792, IN 939), Rene alloys (e.g. Rene N5, Rene 41, Rene 80, Rene 108, Rene 142, Rene 220), Haynes alloys (282), Mar M, CM 247, CM 247 LC, C263, 718, X-750, 25 ECY 768, 282, X45, PWA 1480, PWA 1483, PWA 1484, CMSX single crystal alloys (e.g., CMSX-4, CMSX-8, CMSX-10), GTD 111, GTD 222, MGA 1400, MGA 2400, PSM 116, Mar-M-200, Udimet 600, Udimet 500 and titanium aluminide. The terms “metal,” “metallic material,” “alloy,” and “metal alloy” are used herein in a general sense to describe pure metals, semi-pure metals and metal alloys.

The protective layer 6 of FIG. 2 (as well as in other embodiments described and implied below) may be a ceramic layer suitable for use as a thermal barrier coating (TBC), including TBCs well known in the relevant art. Such ceramic coatings generally have low thermal conductivity and include metal oxides such as zirconia (ZrO₂) partially or fully stabilized by yttria (Y₂O₃), magnesia (MgO) or other oxides. In some embodiments the protective layer 6 may include a yttri-stabilized zirconia (YSZ).

The adhesive bonding layer 14 of FIG. 2 (as well as in other embodiments described an implied below) contains one or more inorganic compounds that may include metal oxides, metal halides, metal oxometallates, metal carbonates, as well as elemental metals and metalloids of Groups IIA, IIIB, IVB, VB, VIB, VIIB, VIIIB, IB, IIB, IIIA, IVA, VA of the Period Table, lanthanides, and non-metals such as boron and carbon. As explained below in greater detail, the adhesive bonding layer 14 is formed by heating a protective bonding composition into a molten material in contact with a metal-containing surface, and then the molten material is allowed to cool and solidify into a deposit having low detachability from the metal-containing surface.

To attain the desired low detachability of the adhesive bonding layer 14, the protective bonding composition is formulated to contain certain mixtures of compounds (described below in greater detail) which react in the heated environment of the molten material to form at least one oxygen-containing compound that promotes the bonding of the adhesive bonding layer 14 to the metallic substrate 2, the protective layer 6, or both.

In some embodiments the oxygen-containing compound is selected from a spinel compound, a perovskite compound, a cuspidine compound, and mixtures thereof. In some embodiments the oxygen-containing compound is selected from MgAlCrO₄, FeCrO₄, CaTiO₃, Ca₄(Si₂O₇)(F,OH)₂, and mixtures thereof.

The term “spinel compound” is used herein in a general sense to describe an inorganic compound or mineral of the general formula MgAlMO₄ wherein the element “M” refers to a metallic element such as Al or a transition metal such as Cr. The term “spinel compound” is also used herein in the same manner as this term is commonly understood in the relevant art. The term “perovskite compound” is used herein in a general sense to describe an inorganic compound or mineral of the general formula CaTiO₃. The term “perovskite compound” is also used herein in the same manner as this term is commonly understood in the relevant art. The term “cuspidine compound” is used herein in a general sense to describe an inorganic compound or mineral of the general formula Ca₄(Si₂O₇)(F,OH)₂. The term “cuspidine compound” is also used herein in the same manner as this term is commonly understood in the relevant art.

In some embodiments the oxygen-containing compound is believed to enhance adhesion between the adhesive bonding layer 14 and the metallic substrate 2, the protective layer 6, or both, by forming rigid crystalline structures serving as hooks or anchors to which the respective materials can inter-bond. FIG. 6 is a photograph illustrating such rigid crystalline structures in the form of spear-like cuspidine crystals 52 that are chemically anchored to a surface of a metallic substrate 50. The spear-like protrusions of the cuspidine crystals 52 can then rigidly bond to an upper layer (e.g., an adhesive bonding layer 14 or a protective layer 6) that is subsequently or concurrently formed to produce a multi-layer article in which the outer protective layer has low detachability.

As also illustrated in FIG. 2, in some embodiments the multi-layer article 1 may contain a plurality of chemical anchors 16 bonded to the adhesive bonding layer 14 and to at least one of the metallic substrate 2 and the protective layer 6. In the embodiment of FIG. 2 the plurality of chemical anchors 16 form inter-layer bonds such that one portion of the chemical anchors 16 is bonded to the adhesive bonding layer 14 and another portion of the chemical anchors is bonded to the metallic substrate 2.

FIG. 3 is a cross-sectional view of a multi-layer article 3 containing a metallic substrate 2, a bond coat layer 4, an adhesive bonding layer 14, and a protective layer 6, according to one embodiment. The bond coat layer 4 may be in the form of a metallic coating of the general formula MCrAlX wherein “M” is a Group VIIIB element such as Co, Ni, or a mixture thereof, and “X” is a rare earth elements such as Y, Hf, W, Zr, La, or a mixture thereof. In other embodiments the bond coat layer 4 may be in the form of a diffusion aluminide coating such as NiAl or a modified NiAl that includes an element such as Cr, Pt, Rh or Pd. FIG. 3 also illustrates the possible presence of a plurality of chemical anchors 16 bonded to the adhesive bonding layer 14 and to the bond coat layer 4 by forming inter-layer bonds such that one portion of the chemical anchors 16 is bonded to the adhesive bonding layer 14 and another portion of the chemical anchors 16 is bonded to the bond coat layer 4.

In some embodiments, for example, the metallic substrate 2 of FIG. 2 may be in the form of a superalloy substrate, the bond coat layer 4 may be in the form of a MCrAlY bond coat layer and the protective layer 6 may be in the form of a ceramic TBC layer.

FIGS. 4 and 5 illustrate other embodiments wherein the plurality of chemical anchors 16 enhance adhesion of the multi-layer articles 5, 7 by forming inter-layer bonds such that a first portion of the chemical anchors 16 is bonded to the metallic substrate 2, a second portion of the chemical anchors 16 is bonded to a residual portion 18 of an adhesive bonding layer, and a third portion of the chemical anchors 16 is bonded to the protective layer 6.

FIG. 4 is a cross-sectional view of a multi-layer article 5 containing a metallic substrate 2, a protective layer 6, and a plurality of chemical anchors 16 inter-bonded to both the metallic substrate 2 and to the protective layer 6. In some embodiments the multi-layer article 5 may also contain a residual portion 18 of an adhesive bonding layer such that the chemical anchors 16 inter-bond to all three of the metallic substrate 2, the protective layer 6 and the residual portion 18 of an adhesive bonding layer.

FIG. 5 is a cross-sectional view of a multi-layer article 7 containing a metallic substrate 2, a bond coat layer 4, a protective layer 6, and a plurality of chemical anchors 16 inter-bonded to both the bond coat layer 4 and to the protective layer 6. In some embodiments the multi-layer article 7 may also contain a residual portion 18 of an adhesive bonding layer such that the chemical anchors 16 inter-bond to all three of the bond coat layer 4, the protective layer 6 and the residual portion 18 of an adhesive bonding layer.

FIG. 7 illustrates process steps of a method for forming the multi-layer article 1 of FIG. 2, according to one embodiment. In Step 1 of FIG. 7, a protective bonding composition 20 is deposited onto a surface of a metallic substrate 2, and an energy beam 22′ is traversed over the surface of the protective bonding composition 20 to form a melt pool 24 that is then allowed to cool and solidify into an adhesive bonding layer 14 affixed to the metallic substrate 2. In some embodiments, depending upon the content of the protective bonding composition 20, the resulting article may also contain a plurality of chemical anchors 16 inter-bonded to both the metallic substrate 2 and to the adhesive bonding layer 14. In Step 2 of FIG. 7, a ceramic powder 26 is then deposited onto a surface of the adhesive bonding layer 14, and an energy beam 22″ is traversed over the surface of the ceramic powder 26 to form a region 28 of sintering ceramic powder which upon cooling forms a protective ceramic layer 6.

FIG. 8 illustrates process steps of a method for forming the multi-layer article 3 of FIG. 3, according to one embodiment. In Step 1 of FIG. 8, a MCrAlY powder 30 is deposited onto a surface of a metallic substrate 2, and a protective bonding composition 20 (as, for example, a powder) is deposited onto the layer of MCrAlY powder 30, and an energy beam 22′ is traversed over the surface of the resulting multi-powder layer to form a melt pool 32 that is then allowed to cool and solidify into a MCrAlY bond coat layer 4 bonded to the metallic substrate 2 and covered by an adhesive bonding layer 14 affixed to the bond coat layer 4. In some embodiments, depending upon the content of the protective bonding composition 20, the resulting article may also contain a plurality of chemical anchors 16 inter-bonded to both the bond coat layer 4 and to the adhesive bonding layer 14. In other embodiments, the MCrAlY powder 30 and the protective bonding composition 20 may be deposited onto the surface of the metallic substrate 2 as a mixture of powders (as opposed to the separate multi-layers illustrated in FIG. 8). In Step 2 of FIG. 8, a ceramic powder 26 is then deposited onto a surface of the adhesive bonding layer 14, and an energy beam 22″ is traversed over the surface of the ceramic powder 26 to form a region 28 of sintering ceramic powder which upon cooling forms a protective ceramic layer 6.

FIG. 9 illustrates process steps of a method for forming the multi-layer article 7 of FIG. 5, according to one embodiment. In Step 1 of FIG. 9, a MCrAlY powder 30 is deposited onto a surface of a metallic substrate 2, and a protective bonding composition 20 (as, for example, a powder) is deposited onto the layer of MCrAlY powder 30, and an energy beam 22′ is traversed over the surface of the resulting multi-powder layer to form a melt pool 32 that is then allowed to cool and solidify into a MCrAlY bond coat layer 4 bonded to the metallic substrate 2 and covered by an adhesive bonding layer 14 affixed to the bond coat layer 4. In some embodiments, depending upon the content of the protective bonding composition 20, the resulting article may also contain a plurality of chemical anchors 16 inter-bonded to both the bond coat layer 4 and to the adhesive bonding layer 14. In other embodiments, the MCrAlY powder 30 and the protective bonding composition 20 may be deposited onto the surface of the metallic substrate 2 as a mixture of powders (as opposed to the separate multi-layers illustrated in FIG. 8.

Step 2 of FIG. 9 involves removal of a portion of the adhesive bonding layer 14 to form a residual portion 18 of the adhesive bonding layer 14 such that some portions of the chemical anchors 16 are exposed in an upward direction. Chemical and/or mechanical methods known in the relevant art for removing slag layers may be used to accomplish the removal of a portion of the adhesive bonding layer 14 in Step 2.

In Step 3 of FIG. 9, a ceramic powder 26 is then deposited onto a surface of the article formed in Step 2, and an energy beam 22″ is traversed over the surface of the ceramic powder 26 to form a region 28 of sintering ceramic powder which upon cooling forms a protective ceramic layer 6. Because the removal Step 2 exposes portions of the chemical anchors 16 in an upward direction, the Step 3 deposition of the protective ceramic layer 6 can occur such that the chemical anchors 16 form inter-layer bonds in which a first portion of the chemical anchors 16 is bonded to the metallic substrate 2, a second portion of the chemical anchors 16 is bonded to the residual portion 18 of adhesive bonding layer 14, and a third portion of the chemical anchors 16 is bonded to the protective ceramic layer 6.

Protective bonding compositions 20 may contain inorganic compounds such as metal oxides, metal halides, metal oxometallates, metal carbonates, a mixtures thereof—as well as elemental metals, lanthanides and metalloids. Protective bonding compositions 20 may also include organic compounds such as high-molecular weight hydrocarbons (e.g., beeswax, paraffin), carbohydrates (e.g., cellulose), natural and synthetic oils (e.g., palm oil), organic reducing agents (e.g., charcoal, coke), carboxylic acids and dicarboxylic acids (e.g., abietic acid, isopimaric acid, neoabietic acid, dehydroabietic acid, rosins), carboxylic acid salts (e.g., rosin salts), carboxylic acid derivatives (e.g., dehydro-abietylamine), amines (e.g., triethanolamine), alcohols (e.g., high polyglycols, glycerols), natural and synthetic resins (e.g., polyol esters of fatty acids), and other organic compounds, as well a mixture thereof.

The term “metal oxides” is used herein in a general sense to describe compounds having the general formula M_(a)O_(b) in which the variable “M” represents a metal atom, and the variables “a” and “b” represent integers greater than zero. Non-limiting examples of metal oxides include compounds such as Li₂O, BeO, B₂O₃, B₆O, MgO, Al₂O₃, SiO₂, CaO, Sc₂O₃, TiO, TiO₂, Ti₂O₃, VO, V₂O₃, V₂O₄, V₂O₅, Cr₂O₃, CrO₃, MnO, MnO₂, Mn₂O₃, Mn₃O₄, FeO, Fe₂O₃, Fe₃O₄, CoO, Co₃O₄, NiO, Ni₂O₃, Cu₂O, CuO, ZnO, Ga₂O₃, GeO₂, As₂O₃, Rb₂O, SrO, Y₂O₃, ZrO₂, NiO, NiO₂, Ni₂O₅, MoO₃, MoO₂, RuO₂, Rh₂O₃, RhO₂, PdO, Ag₂O, CdO, In₂O₃, SnO, SnO₂, Sb₂O₃, TeO₂, TeO₃, Cs₂O, BaO, HfO₂, Ta₂O₅, WO₂, WO₃, ReO₃, Re₂O₇, PtO₂, Au₂O₃, La₂O₃, CeO₂, Ce₂O₃, and mixtures thereof, to name a few. The term “metal oxides” is also used herein in the same manner as this term is commonly understood in the relevant art.

The term “metal halides” is used herein in a general sense to describe compounds containing a metal atom and at least one halogen atom. Non-limiting examples of metal halides include compounds such as LiF, LiCl, LiBr, LiI, Li₂NiBr₄, Li₂CuCl₄, LiAsF₆, LiPF₆, LiAlCl₄, LiGaCl₄, Li₂PdCl₄, NaF, NaCl, NaBr, Na₃AlF₆, NaSbF₆, NaAsF₆, NaAuBr₄, NaAlCl₄, Na₂PdCl₄, Na₂PtCl₄, MgF₂, MgCl₂, MgBr₂, AlF₃, KCl, KF, KBr, K₂RuCl₅, K₂IrCl₆, K₂PtCl₆, K₂PtCl₆, K₂ReCl₆, K₃RhCl₆, KSbF₆, KAsF₆, K₂NiF₆, K₂TiF₆, K₂ZrF₆, K₂PtI₆, KAuBr₄, K₂PdBr₄, K₂PdCl₄, CaF₂, CaF, CaBr₂, CaCl₂, CaI₂, ScBr₃, ScCl₃, ScF₃, ScI₃, TiF₃, VCl₂, VCl₃, CrCl₃, CrBr₃, CrCl₂, CrF₂, MnCl₂, MnBr₂, MnF₂, MnF₃, MnI₂, FeBr₂, FeBr₃, FeCl₂, FeCl₃, FeI₂, CoBr₂, CoCl₂, CoF₃, CoF₂, CoI₂, NiBr₂, NiCl₂, NiF₂, NiI₂, CuBr, CuBr₂, CuCl, CuCl₂, CuF₂, CuI, ZnF₂, ZnBr₂, ZnCl₂, ZnI₂, GaBr₃, Ga₂Cl₄, GaCl₃, GaF₃, GaI₃, GaBr₂, GeBr₂, GeI₂, GeI₄, RbBr, RbCl, RbF, RbI, SrBr₂, SrCl₂, SrF₂, SrI₂, YCl₃, YF₃, YI₃, YBr₃, ZrBr₄, ZrCl₄, ZrI₂, YBr, ZrBr₄, ZrCl₄, ZrF₄, ZrI₄, NbCl₅, NbF₅, MoCl₃, MoCl₅, RuI₃, RhCl₃, PdBr₂, PdCl₂, PdI₂, AgCl, AgF, AgF₂, AgSbF₆, AgI, CdBr₂, CdCl₂, CdI₂, InBr, InBr₃, InCl, InCl₂, InCl₃, InF₃, InI, InI₃, SnBr₂, SnCl₂, SnI₂, SnI₄, SnCl₃, SbF₃, SbI₃, CsBr, CsCl, CsF, CsI, BaCl₂, BaF₂, BaI₂, BaCoF₄, BaNiF₄, HfCl₄, HfF₄, TaCl₅, TaF₅, WCl₄, WCl₆, ReCl₃, ReCl₅, IrCl₃, PtBr₂, PtCl₂, AuBr₃, AuCl, AuCl₃, AuI, KAuCl₄, LaBr₃, LaCl₃, LaF₃, LaI₃, CeBr₃, CeCl₃, CeF₃, CeF₄, CeI₃, and mixtures thereof, to name a few. The term “metal halides” is also used herein in the same manner as this term is commonly understood in the relevant art.

The term “metal oxometallates” is used herein in a general sense to describe compounds having the general formula M_(a)X_(b)O_(c) in which the variable “M” represents a metal atom, the variable “X” represents a metal or non-metal atom, and the variables “a,” “b,” and “c” represent integers greater than zero. Non-limiting examples of metal oxometallates include compounds such as LiIO₃, LiBO₂, Li₂SiO₃, LiClO₄, Na₂B₄O₇, NaBO₃, Na₂SiO₃, NaVO₃, Na₂MoO₄, Na₂SeO₄, Na₂SeO₃, Na₂TeO₃, K₂SiO₃, K₂CrO₄, K₂Cr₂O₇, CaSiO₃, BaMnO₄, and mixtures thereof, to name a few. The term “metal oxometallates” is also used herein in the same manner as this term is commonly understood in the relevant art.

The term “metal carbonates” is used herein in a general sense to describe compounds containing a metal atom and at least one carbonate group. Non-limiting example of metal carbonates include compounds such as Li₂CO₃, Na₂CO₃, NaHCO₃, MgCO₃, K₂CO₃, CaCO₃, Cr₂(CO₃)₃, MnCO₃, CoCO₃, NiCO₃, CuCO₃, Rb₂CO₃, SrCO₃, Y₂(CO3)₃, Ag₂CO₃, CdCO₃, In₂(CO₃)₃, Sb₂(CO₃)₃, C₂CO₃, BaCO₃, La₂(CO₃)₃, Ce₂(CO₃)₃, NaAl(CO₃) (OH)₂, and mixtures thereof, to name a few. The term “metal carbonates” is also used herein in the same manner as this term is commonly understood in the relevant art.

In some embodiments TBC 6 adhesion to a MCrAlY bond-coat underlayer 4 (such as, for example, in FIGS. 3 and 5) is improved by employing a protective bonding composition 20 containing MgO and Al₂O₃. It is known in the welding industry that slag is particularly difficult to remove from chromium-bearing substrates, or from deposits made with a chromium-bearing filler, or from deposits utilizing chromium oxide in the flux. See, e.g., Oladipupo, A. O., “Slag Detachability from Submerged Arc Welds,” Doctoral Thesis (Massachusetts Institute of Technology) February 1987. Fluxes with magnesium oxide and alumina are particularly problematic due to the formation of chromium spinels such as iron chromate and magnesium aluminum chromate by reactions such as:

MgO+Al₂O₃→MgAlCrO₄

These spinels represent solid reaction products that embed and attach to the underlying metallic substrate and can therefore serve as chemical anchors 16 that can greatly increase attachability (bond integrity) in multi-layer articles of the present disclosure.

Protective bonding compositions 20 in some embodiments contain MgO and Al₂O₃ in respective proportions such that a molten mixture containing the composition 20 and Cr forms MgAlCrO₄. In some embodiments a molar ratio of the MgO to the Al₂O₃ in the protective bonding composition 20 ranges from about 1.5:1 to about 1:1.5, or from about 1.3:1 to about 1:1.3, or from about 1.1:1 to about 1:1.1 respectively. In other embodiments the molar ratio of the MgO to the Al₂O₃ is about 1:1.

Some MgO/Al₂O₃-containing compositions 20 comprise at least one of: (1) greater than about 25 percent by weight of MgO; and (2) greater than out 25 percent by weight of Al₂O₃, based on a total weight of the protective bonding composition 20. In other embodiments compositions 20 comprise at least one of: (1) greater than about 35 percent by weight of MgO; and (2) greater than about 35 percent by weight of Al₂O₃, based on a total weight of the protective bonding composition 20. In some embodiments the MgO/Al₂O₃-containing compositions 20 may further comprise Cr, such as for example greater than about 10 percent by weight of Cr or greater than about 15 percent by weight of Cr. In other embodiments the MgO/Al₂O₃-containing compositions 20 may further comprise at least one selected from the group consisting of Cr, CrO₂, Cr₂O₃ and CrO₃.

Some MgO/Al₂O₃-containing compositions 20 further contain TiO₂, SiO₂ and ZrO₂, such that a sum of the weights of the Al₂O₃, TiO₂, SiO₂ and the ZrO₂ is less than about 6.5 percent by weight or more than about 12 percent by weight, based on a total weight of the protective bonding composition 20. Still in other embodiments the MgO/Al₂O₃-containing compositions 20 further contain at least one of: (1) CaO and TiO₂ in respective proportions such that a molten mixture containing the composition 20 also forms CaTiO₃; and (2) CaF₂ and SiO₂ in respective proportions such that a molten mixture containing the composition 20 also forms Ca₄(Si₂O₇)(F,OH)₂.

Flux compositions containing calcium oxide and rutile are also known in the relevant art to be problematic (in terms of slag detachability from a weld) and to form calcium titanate perovskites by reactions such as:

CaO+TiO₂→CaTiO₃

These perovskites may also act as chemical anchors 16 that reduce detachability. The inventors have recognized that protective bonding compositions 20 that contain mixtures of compounds selected from MgO, Al₂O₃, CaO and TiO₂ can increase TBC 6 adherence to chromium-containing MCrAlY bond coats 4.

Some protective bonding compositions 20 contain CaO and TiO₂ in respective proportions such that a molten mixture containing the composition 20 forms CaTiO₃. In some embodiments a molar ratio of the CaO to the TiO₂ ranges from about 1.5:1 to about 1:1.5, or from about 1.3:1 to about 1:1.3, or from about 1.1:1 to about 1:1.1 respectively. In other embodiments the molar ratio of the CaO to the TiO₂ is about 1:1.

Some CaO/TiO₂-containing compositions 20 comprise at least one of: (1) greater than about 5 percent by weight of the CaO; and (2) greater than about 5 percent by weight of the TiO₂, based on a total weight of the protective bonding composition 20. In other embodiments compositions 20 comprise at least one of: (1) greater than about 10 percent by weight of the CaO; and (2) greater than about 10 percent by weight of the TiO2, based on a total weight of the protective bonding composition 20.

Some CaO/TiO₂-containing compositions 20 further contain SiO₂, Al₂O₃ and ZrO₂, such that a sum of the weights of the Al₂O₃, TiO₂, SiO₂ and the ZrO₂ is less than about 6.5 percent by weight or more than about 12 percent by weight, based on a total weight of the protective bonding composition 20. Still in other embodiments the CaO/TiO₂-containing compositions 20 further contain at least one of: (1) CaF₂ and SiO₂ in respective proportions such that a molten mixture containing the composition 20 also forms Ca₄(Si₂O₇)(F,OH)₂; and (2) MgO and Al₂O₃ in respective proportions such that a molten mixture containing the composition 20 and Cr forms MgAlCrO₄.

Flux compositions containing calcium fluoride and silica are also known in the relevant art to be problematic and to form cuspidine [Ca₄(Si₂O₇)(F,OH)₂] which also hinders slag removal. Cuspis is Greek and means “spear” which is related to the shape of crystalline cuspidine (see FIG. 6) which is likely responsible for its anchoring effect when contained in slags.

Some protective bonding compositions 20 of the present disclosure contain CaF₂ and SiO₂ in respective proportions such that a molten mixture containing the composition 20 forms Ca₄(Si₂O₇)(F,OH)₂. In some embodiments a molar ratio of the CaF₂ to the SiO₂ ranges from about 1.5:1 to about 2.5:1, or from about 1.7:1 to about 2.3:1, or from about 1.9:1 to about 2.1:1, respectively. In other embodiments the molar ratio of the CaF₂ to the SiO₂ is about 2:1 respectively.

Some CaF₂/SiO₂-containing compositions 20 comprise at least one of: (1) greater than about 25 percent by weight of CaF₂; and (2) greater than about 25 percent by weight of SiO₂. In other embodiments CaF₂/SiO₂-containing compositions 20 comprise at least one of: (1) greater than about 35 percent by weight of CaF₂; and (2) greater than about 35 percent by weight of SiO₂.

Some CaF₂/SiO₂-containing compositions 20 further contain Al₂O₃, TiO₂ and ZrO₂, such that a sum of the weights of the Al₂O₃, TiO₂, SiO₂ and the ZrO₂ is less than about 6.5 percent by weight or more than about 12 percent by weight, based on a total weight of the protective bonding composition 20. Still in other embodiments the CaF₂/SiO₂-containing compositions 20 further contain at least one of: (1) CaO and TiO₂ in respective proportions such that the molten mixture also forms CaTiO₃; and (2) MgO and Al₂O₃ in respective proportions such that a molten mixture containing the composition 20 and Cr forms MgAlCrO₄.

While various embodiments of the present invention have been shown and described herein, it will be obvious that such embodiments are provided by way of example only. Numerous variations, changes and substitutions may be made without departing from the invention herein. 

The invention claimed is:
 1. A multi-layer article, comprising: a metallic substrate; a protective layer; and an adhesive bonding layer comprising an oxygen-containing compound that bonds the adhesive bonding layer to the metallic substrate, the protective layer, or both.
 2. The article of claim 1, further comprising a plurality of anchors bonded to the adhesive bonding layer and to at least one of the metallic substrate and the protective layer, wherein: the anchors comprise the oxygen-containing compound; and a structure of the anchors is effective to adhere the metallic substrate, the protective layer, or both, to the adhesive bonding layer by forming inter-layer linkages such that one portion of the anchors is attached to the adhesive bonding layer and another portion of the anchors is attached to the metallic substrate or to the protective layer.
 3. The article of claim 1, comprising: a superalloy substrate; a MCrAlY bond coat layer bonded to a surface of the superalloy substrate; the adhesive bonding layer bonded to a surface of the MCrAlY bond coat layer; and a ceramic thermal barrier layer bonded to a surface of the adhesive bonding layer.
 4. The article of claim 1, comprising: a superalloy substrate; the adhesive bonding layer bonded to a surface of the superalloy substrate; and a ceramic thermal barrier layer bonded to a surface of the adhesive bonding layer.
 5. The article of claim 1, wherein the oxygen-containing compound is at least one selected from the group consisting of a spinel compound, a perovskite compound, and a cuspidine compound.
 6. The article of claim 1, wherein the oxygen-containing compound is at least one selected from the group consisting of MgAlCrO₄, FeCrO₄, CaTiO₃, and Ca₄(Si₂O₇)(F,OH)₂.
 7. The article of claim 1, wherein the adhesive bonding layer is formed from a protective bonding composition comprising at least one of: a mixture of MgO and Al₂O₃ in respective proportions such that an adhesive bonding layer comprising Cr further comprises MgAlCrO₄; a mixture of CaO and TiO₂ in respective proportions such that the adhesive bonding layer comprises CaTiO₃; and a mixture of CaF₂ and SiO₂ in respective proportions such that the adhesive bonding layer comprises Ca₄(Si₂O₇)(F,OH)₂.
 8. The article of claim 7, satisfying at least one of the following conditions: (i) the protective bonding composition comprises at least one of greater than about 25 percent by weight of the MgO, and greater than about 25 percent by weight of the Al₂O₃; (ii) the protective bonding composition comprises at least one of greater than about 5 percent by weight of the CaO, and greater than about 5 percent by weight of the TiO₂; and (iii) the protective bonding composition comprises at least one of greater than about 25 percent by weight of the CaF₂, and greater than about 20 percent by weight of the SiO₂, based on a total weight of the protective bonding composition.
 9. A multi-layer article, comprising: a metallic layer; a protective layer; and a plurality of anchors bonded to both the metallic layer and the protective layer, wherein: the anchors comprise an oxygen-containing inorganic compound; and a structure of the anchors is effective to adhere the metallic layer to the protective layer by forming inter-layer linkages such that one portion of the anchors is attached to the metallic layer and another portion of the anchors is attached to the protective layer.
 10. The article of claim 9, further comprising an adhesive bonding layer disposed between the metallic layer and the protective layer and in direct contact with the anchors, wherein the anchors form the inter-layer linkages such that a first portion of the anchors is attached to the metallic layer, a second portion of the anchors is attached to the adhesive bonding layer, and a third portion of the anchors is attached to the protective layer.
 11. The article of claim 9, wherein the oxygen-containing inorganic compound is at least one selected from the group consisting of a spinel compound, a perovskite compound, and a cuspidine compound.
 12. The article of claim 9, wherein the oxygen-containing inorganic compound is at least one selected from the group consisting of MgAlCrO₄, FeCrO₄, CaTiO₃, and Ca₄(Si₂O₇)(F,OH)₂.
 13. A method for forming a multi-layer article of claim 1, the method comprising: heating a protective bonding composition to form a molten material in contact with a metal-containing surface; allowing the molten material to cool and solidify into the adhesive bonding layer affixed to the metal-containing surface; depositing a ceramic material onto the adhesive bonding layer; and heating the ceramic material to form the protective layer affixed to the adhesive bonding layer, to form the multi-layer article.
 14. The method of claim 13, wherein the protective bonding composition comprises at least two selected from the group consisting of MgO, Al₂O₃, CaO, TiO₂, CaF₂ and SiO₂.
 15. The method of claim 13, wherein the protective bonding composition comprises MgO and Al₂O₃ in respective proportions such that the molten material in the presence of Cr contains MgAlCrO₄.
 16. The method of claim 15, wherein a molar ratio of the MgO to the Al₂O₃ ranges from about 1.5:1 to about 1:1.5 respectively.
 17. The method of claim 15, wherein the protective bonding composition comprises at least one of: greater than about 25 percent by weight of the MgO; and greater than about 25 percent by weight of the Al₂O₃, based on a total weight of the protective bonding composition.
 18. The method of claim 13, wherein the protective bonding composition comprises CaO and TiO₂ in respective proportions such that the molten material contains CaTiO₃.
 19. The method of claim 18, wherein a molar ratio of the CaO to the TiO₂ ranges from about 1.5:1 to about 1:1.5 respectively.
 20. The method of claim 18, wherein the protective bonding composition comprises at least one of: greater than about 5 percent by weight of the CaO; and greater than about 5 percent by weight of the TiO₂, based on a total weight of the protective bonding composition.
 21. The method of claim 13, wherein the protective bonding composition comprises CaF₂ and SiO₂ in respective proportions such that the molten material contains Ca₄(Si₂O₇)(F,OH)₂.
 22. The method of claim 21, wherein a molar ratio of the CaF₂ to the SiO₂ ranges from about 1.5:1 to about 2.5:1 respectively.
 23. The method of claim 21, wherein the protective bonding composition comprises at least one of: greater than about 25 percent by weight of the CaF₂; and greater than about 20 percent by weight of the SiO₂, based on a total weight of the protective bonding composition.
 24. The method of claim 13, wherein the metal-containing surface is a metallic substrate or is a bond coat layer affixed to a surface of the metallic substrate.
 25. The method of claim 13, further comprising removing a portion of the adhesive bonding layer before the depositing of the ceramic material, such that: anchors contained in the adhesive bonding layer are not removed and remain attached to the metal-containing surface; and exposed portions of the anchors become attached to the protective layer during the heating of the ceramic material. 